It is well established that Borrelia burgdorferi, the etiologic agent of Lyme disease, adapts to distinct environments as it moves between an arthropod vector and mammalian hosts. B. burgdorferi modulates gene expression and protein synthesis in response to environmental cues temperature, pH, O2, CO2 and other unknown host factors. CO2 is a byproduct of cellular respiration and levels fluctuate within the mammalian host potentially signaling to pathogenic organisms for host adaptive responses. Pathogens utilize CO2 and HCO3 detection for activation of toxin expression or induction of a cAMP signaling pathway. We hypothesize that B. burgdorferi employs similar mechanisms to adequately adapt for pathogenesis in the mammalian host. Our Preliminary Data suggests CO2 serves as a signal to B. burgdorferi to regulate the production of a transcriptional regulator and the expression of genes that are important for infectivity. Two borrelial regulatory systems, the Rrp2-RpoN-RpoS regulatory system and the BosR protein, are altered in response to CO2 suggesting that this environmental cue is critical for B. burgdorferi to sense, adapt, and survive in the mammalian host. BosR, borrelial oxidative stress regulator, is post-transcriptionally regulated in response to CO2 and interacts with the rpoS promoter potential resulting in CO2 transcriptional regulation of rpoS and RpoS-dependent genes. To this end we propose the following Specific Aims: (1) Ascertain the mechanism utilized by B. burgdorferi to sense and respond to environmental CO2;(2) Identify genes and proteins regulated by CO2 in infectious B. burgdorferi. In the proposed studies, the putative borrelial adenylate cyclase, cyaB, has been deleted and the CO2 regulation will be evaluated, as well as inhibition of cAMP accumulation, relative to the parent strain. We will determine how cyaB activity contributes to infectivity of B. burgdorferi via bioluminescence in vivo imaging. Recently we have used in vivo imaging to detect light emitting (i.e., luciferase [luc] expressing) infectiou B. burgdorferi following experimental infection. The advantage of this approach is that B. burgdorferi can be visualized numerous times in live mice over time to track the infectious process. This exciting approach provides a powerful non-invasive, real time modality to evaluate infectivity in a temporal and spatial manner. In addition, transcriptomic and proteomic technologies will be utilized to generate a comprehensive subset of genes and proteins that are responsive to CO2 with the long term goal that this will provide a platform to identify novel virulence determinants and potential therapeutic targets. A mechanism of direct detection of an environmental cue that is sensed by B. burgdorferi has not yet been characterized. The proposed work herein will characterize how CO2 sensing contributes to the complex regulation engaged by B. burgdorferi as it traverses through its complex life cycle.

Public Health Relevance

Borrelia burgdorferi, the etiologic agent of Lyme disease, is the most common arthropod-borne infectious agent in the United States, and, as such, represents an important Public Health issue. The studies described in this application are designed to build on published studies demonstrating CO2 expression of genes important for infectivity and that light emitting B. burgdorferi can be detected in vivo following experimental infection. We will characterize the mechanism of CO2 sensing by an adenylate cyclase gene and its role in the pathogenic potential of B. burgdorferi.